The present invention relates to a fuel-injection nozzle for internal combustion engines which consists of a nozzle housing terminating in a nozzle tip and a pintle which is guided in said housing and is conical at its lower end, it being pressed under spring action against a conical valve seat in the nozzle tip, the conical valve seat having a plurality of spray holes covered by the conical end of the pintle and passing into a blind hole, the pintle, in a first phase of the stroke lifting off from the valve seat under the pressure of the fuel fed against the force of a first spring and coming against a stop which, in its turn, is displaceable, in a second phase of the stroke, against the force of a second spring, and, at the end of the first phase of the stroke, the corresponding imaginary cylinder surface area which results in the extension of each spray hole between the conical end of the pintle and the conical valve seat is smaller than the cross-sectional area of the corresponding spray hole, as a result of which there is a first deflection of the flow of fuel in the space between pintle and conical valve seat and a following second deflection upon flow into the spray hole.
From U.S. Pat. No. 5,242,118 an injection nozzle of this type is known in which the cylindrical wall surface in the extension of each spray hole is at most 0.75 times the cross-sectional area of the corresponding spray hole. Due to the special conditions of flow caused in part by this, maximum atomization was obtained with such nozzles during the first phase of the stroke and optimal atomization with sufficient penetration in the second phase of the stroke. However, there was room for further improvement with respect to emission and to combustion noises, particularly in the first phase of the stroke. In view of the future maximum exhaust gas values pursuant to EURO III, further improvements and optimization were also necessary. They were achieved in extensive series of tests, and based on hydrodynamic considerations.
With these considerations the following relationships were established: The slight injection rate necessary during the first phase of the stroke requires the smallest possible needle stroke; this produces, in particular, a reduction in the combustion noise. This small needle stroke leads to an increased pressure loss and the atomization is maximum, which, after ignition, leads to increased emission of particles. However, this pressure loss also reduces the penetration, which, on the one hand, results in a reduction in the emission of hydrocarbons (HC-emissions are produced by contact of the fuel with the wall) but, on the other hand, in a non-uniform distribution of the fuel in the combustion air, and thus causes particle emissions. To this extent an enlargement of the needle stroke would be preferable, but this, in its turn, leads to an increase in the combustion noise. Nevertheless, the size of stroke in the first phase cannot be varied as might be desired; the flow and pressure conditions must always permit the development of the special flow pattern with the double deflection in the immediate vicinity of the entrance into the spray hole which is described in detail in U.S. Pat. No. 5,242,118 which represents the prior art. As soon as the conditions change out of the very narrow limits, the special form of flow cannot develop, or it collapses. As a result, all advantages are lost, since the injection cloud then becomes an injection jet, which leads to a sudden increase in the HC and particle emissions.
In addition to this, there is another difficulty when such nozzles are inclined in the customary manner--and therefore in an engine having two valves per cylinder. Since the spray holes are then no longer the same with respect to the nozzle axis, the pressure losses in the entrance zone and the exit zone of the spray holes and in the hole itself are different.
It is thus the object of the invention to find a way out of this dilemma and to improve the nozzle of the prior art in such a manner that the emission behavior as a whole and therefore all emissions including emissions of noise is further improved.